1. Field of the Invention
The present invention relates to methods and computer programs for automated design and manufacture of custom workholding fixtures or other similar objects requiring machining of substantially unique mounting geometries. More particularly, the present invention concerns a method and computer program providing for substantially automated CAD/CAM design and manufacture of custom workholding fixtures used to locate and secure workpieces or other items on which work, such as, for example, machining, welding, or assembly, is to be performed, wherein computer models of support structures and locating and clamping devices, including dimensions and mounting geometries associated therewith, facilitate development and testing of a workholding concept, production of fixture drawings, and generation and formatting of a corresponding control program for controlling a machine for manufacturing the fixture.
2. Description of the Prior Art
It is often desirable to create a custom workholding fixture to locate and clamp, hold, or otherwise secure parts, workpieces, or other items on which it is desired to perform manufacturing operations such as, for example, machining, welding, or assembly. Unfortunately, developing such a workholding fixture, from design to actual manufacture, can be a slow, expensive, and generally inefficient process.
Presently, fixture creation begins with development of a xe2x80x9cworkholding conceptxe2x80x9d or strategy for holding the workpiece during the manufacturing operations. A common method starts with a support or base structure, typically including, for example, a horizontal mounting plate, a tower structure, an angle plate, a window structure, and other support structures. A designer selects and arranges one or more locating and clamping devices in a manner sufficient to adequately and safely locate and secure the workpiece on the support structure. Such selection and arrangement is made with hard-won experience and is based on such considerations as, for example, the specifications and characteristics of the workpiece, the devices, and the support structure; the particular application and operations to be performed on the workpiece; and the particular circumstances surrounding those operations.
As will be appreciated by those with skill in the art, development of the workholding concept is a custom process for each different workpiece. There are no set standards, meaning every person engaged in this type of work may do things differently. Thus, with little or no standardization, the process can require considerable knowledge and experience in designing and in developing workholding concepts, and can include substantial risks of costly and time-consuming human errors.
Once the workholding concept is complete, it must be implemented to produce the actual workholding fixture. First, detailed design drawings must be produced by a fixture drawing draftsperson, wherein is shown and identified each locating and clamping device in its proper position on the support structure. The drawings must also show and dimension each device""s mounting geometry, including, for example, fastening features or hole patterns, with which the device will be secured to the support structure. Furthermore, all of the mounting geometries usually are dimensioned referenced to a common locating axis on the support structure for manufacturability purposes. If, during production of the drawings, insufficient clearances between devices, the support structure, and the workpiece are discovered, the workholding concept must be re-designed so as to avoid the interference or other problem.
Next, a computer numerical control (CNC) program must be developed by a CNC programmer. The CNC program is based upon the workholding concept and upon the workholding fixture drawings and is therefore similarly unique to each fixture. The CNC program provides the machine code needed to direct a CNC machine to manufacture the support structure, including milling, drilling and tapping or otherwise implementing the mounting geometries for the devices. Additionally, the CNC programmer will develop a tooling list which identifies all tools needed and will group similar steps or steps involving similar tools so as to streamline preparation work by reducing or eliminating redundant or otherwise inefficient or wasteful actions.
Next, a machine operator, using the fixture drawing and the CNC program, prepares the machining operation for making the support structure. This includes verifying the CNC program by loading any required tooling and carefully stepping through the machining of each workpieces"" mounting geometry to ensure that each will be properly made in accordance with the fixture drawing. Typically, there will be only one unique support structure made for each type of workpiece to be held, regardless of the total number of workpieces, necessitating that every step from development of the workholding concept, production of the fixture drawing, programming of the CNC program, and machining of the support structure be absolutely correct or else every instance of the workpiece will be improperly manufactured.
Once the support structure is completed, the various locating and clamping devices can be mounted, after which the support structure is ready to hold the workpiece for the machining, welding, or assembly process.
It will be appreciated that this process is slow, inefficient, and fraught with potential for error. Typically, four skilled people are involved, including the workholding concept designer, the fixture drawing draftsman, the CNC program programmer, and the machine operator. Lead time from start to finish can easily reach or exceed four weeks. Errors committed at any point in the process can be carried through and possibly magnified, and may not be discovered until the support structure is assembled and the workholding devices cannot be properly mounted because of incorrect hole patterns, or, in some cases, the hole patterns may be correct but the workholding device placement may be wrong. Where errors are found, it may be possible to fill incorrect holes and redrill the support structure rather than start anew, though, in either case, time and money is lost.
Due to the above-identified and other problems and disadvantages in the art, a need exists for an improved process for designing and manufacturing custom workholding fixtures.
The present invention provides a distinct advance in the art of methods and computer programs for automated design and manufacture of custom workholding fixtures or other similar objects requiring machining, fabricating, or assembling of substantially unique mounting geometries. More particularly, the present invention provides a method and computer program for substantially automated CAD/CAM design and manufacture of custom workholding fixtures used to locate and secure workpieces on which work, such as, for example, machining, welding, or assembly, is to be performed, wherein computer models of support structures and locating and clamping devices, including dimensions and mounting geometries associated therewith, facilitate development and testing of a workholding concept, production of fixture drawings, and generation and formatting of a corresponding control program for controlling a CNC machine for manufacturing the workholding fixture.
In a preferred embodiment, the present invention is embodied in a computer program stored on and executed by a system comprising a substantially conventional computing device coupled with and operable to direct and control the substantially conventional CNC machine to machine the workholding fixture. The workholding fixture comprises the support structure and one or more of the workholding devices, which may be, for example, swing clamps, work supports, special use clamps, edge clamps, or collet vises, of an electric, hydraulic, or manual nature.
In a preferred embodiment, the computer program supplements existing CAD software, and broadly comprises code segments relating to one or more workholding fixture templates; one or more predefined libraries of support structures, device models, and associated processes; one or more user defined features (UDFs); a CNC post processor; and one or more iconic macros. The fixture templates are provided to facilitate standardization in and streamlining of the design process. The templates can be preset with operation parameters, manufacturing parameters, work cell definitions, tooling definitions, PPRINT settings, and any other settings that may have to be performed with each new CNC program. Thus, rather than beginning each new workholding fixture design from scratch, a user may choose to begin with an existing template and change parameters and otherwise adapt it as needed.
The libraries contain a plurality of computer models or virtual embodiments of a variety of support structures and locating and clamping devices, as well as their associated dimensions and mounting geometries. This allows the user to simply select a desired support structure and one or more desired devices from the library. Because the dimensions and mounting geometries are represented in the models, the computer program is able to facilitate checking for tolerances, clearances, and interferences.
The UDFs are used to capture design and manufacturing intent in a form that can be applied to new designs. Some UDFs are associated with design processes and are used to automatically populate the fixture model with the selected clamping device""s mounting geometry, including, for example, tapped holes, clearance holes, threaded holes, and other features. Other UDFs are associated with manufacturing processes and are used to automatically generate the CNC program required to machine the mounting geometry into or onto the support structure.
A CNC Post Processor is used to output the correctly formatted or otherwise adapted CNC program code for the particular type or brand of CNC machine being used to machine the workholding fixture, thereby allowing the present invention to accommodate a variety of different CNC machines.
The iconic macros are a graphical user interface (GUI) provided to streamline the design and CNC program generation processes. Electronic selection of these icons, as with, for example, a computer mouse or pointer, results in initiation of a corresponding function.
In use and operation, the present invention functions as follows. First, just as in the prior art, a workholding concept must be developed for locating and securing the workpiece. In the present invention, such development is substantially streamlined through computer-based automation using virtual components and simulations. For example, in one embodiment, an appropriate fixture template may be selected to provide a convenient starting point from which to continue the design process.
Thereafter, selection of an appropriate computer-modeled or virtual support structure may be made from a display of a variety of such support structures. Then, selection of one or more appropriate computer-modeled or virtual locating or clamping devices may be made from a display of a variety of such devices. Once selected, the device can be positioned on the selected support structure in a manner sufficient to adequately and safely locate and secure the workpiece. The appropriateness of such choices may be tested immediately and definitively so that, if necessary, a substitution may be made before any further progress in the process occurs.
The devices are modeled using a modeling standard under which all mounting holes may be defined as members of a hole pattern, which reduces the number of user defined features (UDFs). Each UDF can initially be placed referencing a lead member of the hole pattern, and automatically apply itself to the remaining members of the hole pattern. If a standard hole pattern cannot be used to represent an irregular placement of the hole pattern members, then hole pattern tables are used. Furthermore, the lead member of each hole pattern will contain or otherwise be associated with a name or other identifier that describes the type of hole. This feature aids the computer program later in creating the CNC program.
Additionally, as mentioned, all models of clamping or otherwise movable devices will contain appropriate parameters and relations to allow the computer program to check for proper clearances and interferences. Additionally, where applicable, each model will contain features which represent, for example, the point of clamping contact, and which can be used to more easily position the device. Additionally, the computer program uses design variation tables whenever possible, which, it will be appreciated, allows the user to easily replace devices to review a number of design scenarios.
Next, fixture drawings must be produced. Because development of the workholding concept is computerized and integrated with CAD software, rapid and efficient development and testing of the workholding concept is possible along with simultaneous production of the fixture drawings of the finalized concept. Thus, these steps are advantageously and efficiently combined.
The CNC program operable to implement the verified workholding concept must then be generated. Generation of the CNC Program is automatic and performed by the computing device based upon the selected models, their dimensions and mounting geometries, and the fixture drawings.
In the present invention, verification of the CNC code can be minimized because it results from the tested workholding concept. Nevertheless, provision for verification is made in the form of displayable simulated tool motion corresponding to the CNC program. Thus, the CNC program is easily verified without needing to involve the CNC machine itself. This is particularly advantageous where the CNC machine is located remotely from where the CNC program is generated.
Once the CNC program is generated, the CNC post processor formats or otherwise adapts it for the particular CNC machine being used.
In another embodiment of the invention, a user may select a workpiece and one or more clamping devices to hold the workpiece before selecting an appropriate support structure. Specifically, the user first selects and displays a workpiece and then selects and displays one or more clamping devices to hold the workpiece. A support structure is then selected on which to mount the clamping devices and workpiece.
It will be appreciated that the present invention provides a number of substantial advantages over the prior art. For example, whereas the prior art process is slow, inefficient, and fraught with potential for human error, the present invention advantageously maximizes efficiency and minimizes or eliminates error risks by substantially automating and computerizing a great deal of the workholding fixture design and manufacturing process. Furthermore, whereas the prior art process usually requires the involvement of at least four people, including the workholding concept designer, the fixture drawing draftsman, the CNC programmer, and the machine operator, the present invention advantageously and efficiently combines development of the workholding concept with production of the fixture drawings and generation of the machine program, thereby eliminating the draftsman and the programmer and requiring, at most, only two people. This substantial simplification allows for the desirable participation of third-parties, such as customers, in the design and manufacturing process. Additionally, whereas lead time for the prior art process could easily reach or exceed four weeks (not including time required to correct errors), the present invention advantageously reduces lead time to a few days, thereby reducing the design-to-build time by as much as 80%.
These and other important features of the present invention are more fully described in the section titled DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT, below.